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AN ASSESSMENT OF TECHNICAL FACTORS INFLUENCING THE POTENTIAL US--ETC(U)

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AN ASSESSMENT OF TECHNICAL FACTORS

INFLUENCING THE POTENTIAL USE OF RPVs FOR

MINEFIELD DETECTION

Y. MORITA and H. McKENNEYRadar and Optics Division

JULY 1980,./

LCT ESOEC o 8 198o J

U.S. Army Mobility EquipmentResearch and Development CommandFt. Belvoir, VAContract DAAK70-78-C-0198

EVIR ON MEN T AL

__ RSEARCH INSTITUTE OF MICHIGAN__- BOX 8618 ANN ARBOR 0 MICHIGAN 48107

Cq 80 12 04 132

NOTICES

Sosorship. The work reported herein was conducted by theRadar ant Optics Division of the Ervironmental Research Institute ofMichigan for the U.S. Army Mobility Equipment Research' and Develop-ment Command under Contract DAAK 70-7P-C-0198. Contracts and grantsto the Institute for the 'support of sponsored research are adminis-tered through the Office of Contracts Administration.

The views, opinions, and/or findings contained in this reportare those of the authors and should not be construed as an officialDepartment of the Army position, policy, or decision, unless so tes-ionaten bv other documentation.

Distribution. Initial distribution is indicated at the end ofthis document.

Final Disposition. After this document has served its purpose,it may be destroyed. Please do not return it to the EnvironmentalResearch Institute of Michigan.

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AN ASSESSMENT OF TECHNICAL FACTORS INFLUENCING...THE -POTENTIAL USE OF RPVs FOR MINEFIELD P.J., . m ONT Num,,

DETECTIONe 17T" /b_13830(-57-T"

fAA-7&8--dl 98 1S, ' *-,Morita -' McKeney

SPErOINMING OWANDrZnON hADI A" o PPO mesAM ELEMENT 0011O..ECT TASK

Radar and Optics Divi sion, /Environmental A WORK UNIT NUMES

Research Institute of Michigan, P.O. Box 8618,An Anr_ MI 4A1 f7 ____________

U.S. Amy Mobility Equipment Research and /A/Jul ______

Development Command Mine Detection Division, - co, -N

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16. SU P ENNTARY NOTCS

Dr. J.R. Gonano was the contract monitor for this project.

It KEY WOODS (Cowaut 00 rp0Wa Ict i K~aurd:diofti4 bbok aumbr)Mines VegetationRemotely piloted vehiclesTel evisionForward looking infrared system

20 A@STRAC? (Coottwue on mem side if OKmsan and 140*11# I byK block aoe)

. An assessment is made of the use of television and FLIR sensors carriedon RPVs as remote minefield detection systems, based on four major scenariosfor Soviet mine warfare operations involving the use of TM-46 metallic andPM-60 plastic anti-vehicular mines. The RPV system minefield detectioncapability, response time and search rate are functions of the sensorresolution, field of view and sensitivity capabilities; the obscuration IT

00 'OEm , 1473fi EDITION 011 NOV OS ,i OlE,.0V UNCLASSIFIEDSCICNITY CLASSIICATION OF TkiS PAGI(FRs OsoiownIj

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20. ABSTRACT (Continued)due to vegetation, atmospheric attenuation, terrain and weather; the

radiance contrast existing-between mines and background; the airborneplatform characteristics; data link characteristics; the man/machineinterface; and command, control and communication system characteristics.These factors are considered in this study to initially define the mine-field detection capability of currently planned RPVs, to indicate areaswhere additional data is needed to provide a better definition of RPVminefield detection capabilities and to indicate parameters for animproved next generation sensor system.

UNCLASSIFIED.SICWRjITY CLASS, "'CATION OF --. S 04GC Ir h4.w OdD, Emi~r l

ERIN RADAR AND OPTICS DIVISION

PREFACE

The objective of the minefield detection project is to determine

the effectiveness of remote sensing systems and other methods of de-

tecting and identifying mines, minefields, minelaying eauipment, or

minelaying operations, ano to recommend continuing effort on the most

promising methods.

Work under the project concerned with each of the concepts to

be investigated is being performed in a seauence of four major tasks:

(1) identification and screening of promising techniques; (2) pre-

liminary systems analysis and definition of experimental or other

data acquisition systems; (3) acquisition of critical data through

experiment, literature survey, or access to SCI; and (4) evaluation

of conceptual systems for technical performance and military

usefulness.

This is one of a series of reports documenting technical effort

and results achieved during the project. This report covers work

performed under Task 2, Preliminary Systems Analysis of Candidate

Systems.

Dr. J. Roland Gonano monitored the program for MERADCOM, Mr.

Henry McKenney was the ERIM Program Manager, and Mr. Yuji Morita per-

formed the analysis.

I Accession For

DDC TAB

, s-Loc _ _

tt spczia

YRIM RADAR AND OPTICS DIVISION

TABLE OF CONTENTS

Preface........................................................ iii

1. Introduction ................................................ 1I

2. General Considerations ....................................... 3

3. Mine and Minefield Characteristics............................. 5

4. RPV Sensor Considerations.................................... 10

5. Obscurational Factors ....................................... 185.1 Weather 185.2 Terrain 185.3 Vegetation 185.4 Atmospheric Obscuration 27

6. RPV Characteristics ......................................... 30

7. Data Link Characteristics.................................... 33

8. Man/Machine Interface ....................................... 36

9. Command, Control and Communications........................... 37

10. Flight Regimes.............................................. 39

11. Point and Areal Coverage..................................... 43

12. Possible Next Generation Sensor System ........................ 45

13. Findings and Recommendations ................................. 4913.1 General 4913.2 Mines and Minefields 4913.3 Sensors 5013.4 Obscuratlonal Factors 5213.5 RPV Characteristics 5313.6 Data Link Characteristics 5313.7 Man/Machine Interface 5413.8 Command, Control and Communication 5513.9 FlIght Regimes 5

References...................................................... 56

Distribution List ............................................... 57

V

~RIM RADAR AND OPTICS DIVISION

LIST OF FIGURES

Figure 1. Minefield Relationship to FEBA ............................... 4

Figure 2. tine/Background Temperature Contrast ......................... 6

Figure 3. M-15 Mine/Background Temperature Contrast ................... .7

Figure 4. Range of Thermal Contrast Probabilities for DetectionThresholds of 2.O°C and 0.5°C ................................ 8

Figure 5. Geometry for Determining Horizontal Component of

Swath Width on a Slope ...................................... 11

Figure 6. Effect of Gradient on Swath Width ........................... 12

Figure 7. Diagonal Field of View Versus Altitude and SwathWidth ....................................................... 14

Figure 8. Cloud Ceilings Below a Given Altitude ....................... 19

Figure 9. Sensor, Mine and Vegetation Geometry ........................ 20

Figure 10. Geometry for the Overhang Case .............................. 22

Figure 11. Effects of Vegetation Height and Sensor Resolutionon Sensor Altitude and Swath Width .......................... 24

Figure 12. Vegetation Effects on Altitude and Swath Width as a

Function of "a" ........................................ . 25

Figure 13. Vegetation Height and Spacing Effects on Swath Width ........ 2'6

Figure 14. Effect of Vegetation Spacing on Limiting Scan Angle ......... 28

Figure 15. Elevation Tracking Angle and Obstacle Clearance ............. 40

Figure 16. Minefield Search Times ...................................... 42

vii

2ERIM RADAR AND OPTICS DIVISION

LIST OF TABLES

Table 1. FLUR Altitude and Swath Width........................... 16

Table 2. Minimum Altitude in Meters for Electronic Line ofSight Range Fronm RGT in km.............................. 35

ix

~RIM ~ .,cs.vso4' 2ERIMRADAR AND OPTICS DIVISION

AN ASSESSMENT OF TECHNICAL FACTORS INFLUENCING THEPOTENTIAL USE OF RPVs FOR MINEFIELD DETECTION

INTRODUCTION

Previous studies and experiments have lea to the conclusion that

remote detection of Soviet minefields is possible provided that they

are observed from above. This conclusion raises the ouestion as to

whether the currently planned RPV system can detect minefields. This

preliminary study addresses this ouestion and delineates the flight

regimes where detection should be possible, considers factors affect-

ing operational usefulness, and suggests parameters for a next gen-

eration sensor which will enhance the minefield detection capability

of the RPV system. A general description of the RPV, its capabili-

ties and operational and organizational concept are given by Refs.

[1] and [2], which are used as a basis for discussion in this report.

Four major scenarios for Soviet mine warfare operations have been

considered in this study. These scenarios result in the use of mines

for (1) protecting the most exposed flank during meeting engagement;

(2) protecting shoulders during breakthrough; (3) blockino the move-

ment of reinforcements, and (4) supporting a prepared defense. The

first three scenarios are representative of Soviet offensive opera-

tions ana are characterized as hasty operations with mines being in

place a relatively short time. These scenarios have the following

technical implications. Both surface ana buried minefields com-

prised of either plastic or metallic mines must be detected. The

sensor/carrier vehicle combination ideally should have auick reaction

time, and a day/night, all-weather capability. Rapid acauisition

and transmission of information to ensure maximum usability to the

local unit commander is required. Finally, the sensor/carrier vehi-

cle combination must not be unduly vulnerable to enemy actions.

.. RIM RADAR AND OPTICS DIVISION

The RPV system minefield detection capability, response time and

search rate are functions of the sensor resolution, field of view

and sensitivity capabilities; the obscuration aue to vegetation, at-

11spheric attenuation, terrain and weather; the radiance contrast

existing between mines and background; the airborne platform charac-

teristics; data link characteristics; the man/machine interface; and

command, control and communication system characteristics. These

factors are considered in this study to initially define the mine-

field detection capability of currently planned RPVs, to indicate

areas where additional data is needed to provide a better definition

of RPV minefield detection capabilities and to indicate parameters

for an improved next generation sensor system.

2

LRIM RADAR AND OPTICS DIVISION

2GENERAL CONSIDERATIONS

The relationship of the four major scenarios to the forward edge

of the battle area (FEBA) is indicated in Figure 1. Flight times to

potential minefield sites within the division area associated with

scenarios 2 and 3 are not likely to exceed 15 min. Flight times to

potential minefield sites associated with scenarios 1 and 4 are not

likely to exceed 30 minutes.

If we assume that it is possible to locate the RPV remote grounn

terminal so that the masking effect of the terrain and vegetation

features on the line-of-sight aoes not exceed 50 m altitude per kilo-

meter range from the remote ground terminal, then the minimum alti-

tude above ground line permitted for minefielas associatea with

scenarios 2 and 3 is well under 1000 m. and for scenarios 1 and 4 under2500 m.

3

ERIM RADAR AND OPTICS DIVISION

n -

C., cn

41

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44-)

-c t--

,'- ,

- _-

€0

'U

4


3MINE AND MINEFIELD CHARACTERISTICS

The four major scenarios for Soviet mine warfare operations in-

volve the use of the Soviet TM-46 metallic anti-vehicular mine and

the PM60 plastic anti-vehicular mine. These mines are typically in-

stalled in rows with spacing between mines in a row averaging from

4.0 to 5.5 m apart. The rows are spaced from 25 to 50 m apart.

The RPV sensors depend on contrast between the targets and the

background to detect the targets. To date, limited tests have been

conducted to establish a preliminary basis for predicting the con-

trast to be expected from a Soviet minefield with respect to a typi-

cal background.

Although the estimates and the conclusions are drawn on highly

limited data so that high confidence cannot be placed on them, suf-

ficient confidence can be placed in the results to indicate that

minefield detection is possible under proper circumstances. Addi-

tional tests should be run to achieve more confidence.

Tests were performed at MERADCOM to establish the apparent tem-

perature contrast between mines and the background over a diurnal

cycle. The conditions under which the tests were run and the results

are given in Appendix 1 [3]. The results aiven in the appendix have

been replotted in Figures 2 and 3 as apparent temperature differences

between mines and background to indicate the contrast magnitudes.

Detectors typically have sensitivities on the order of a few

tenths of a degree. Assuming that the detectivity threshold is typi-

cally 0.5C then both figures indicate that for all four mines con-

sidered, the apparent temperature difference between mines and back-

ground exceeds the *0.5° contrast reauired a high percentage of the

time. These percentages are plotted as the high values in Figure

4. If we assume a detectivity threshold of 2.0C t ?n the low

values given in Figure 4 apply.

5


w 3

0u=

co,

0 0 Q

C 4

C14

t ~cC~.j i cj .O 0 n

sn~ ~ ~ ~ L Sc L a cu.a4 a.neida

YRIM RADAR AND OPTICS DIVISION

con

aj

CL.

4-JI..

Q CU S

oo

000

EI I.I

os~ L0 a:u.A'~ a.BvAda

RADAR AND OPTICS DIVISION

MINE TYPE

58 88TH-46

49 79

PM-6043 81

First M-1543 80

Second M-15

40 50 60 70 80 90 100

Thermal Contrast Probability()

Figure 4. Range of Thermal Contrast Probabilitiesfor Detection Thresholds of 2.0 0C. and 0.5 0C

8

-ERIM RADAR AND OPTICS DIVISION

Paints used on mines are chosen to have reflectance characteris-

tics similar to that of vegetation in the visible portion of the

spectrL. The poor contrast between mines and a background consist-

ing of vegetation makes the task of detecting mines difficult under

these conditions. On the other hand, contrast may be enhanced on

surfaces where specular returns are possible.

It is expected that television systems will be able to detect

mines under contrast conditions similar to those where photographic

systems are able to detect mines. The performance of television

systems may be poorer than the performance of a passive infrared

system ooerating in the 10 to 14 um region since the sparse data that

exists suggests that the atmospheric extinction coefficient at the

visible wavelengths can be as much as an order of magnitude higher

for altitudes up to 100 m under conditions of ground fog and haze

[4]. There is little data on variations in extinction coefficients

as a function of altitude; collection of more data appears to be

warran tea.

9

LIM RAoAR AND OPTICS DIVISION

4RPV SENSOR CONSIDERATIONS

Experience has Shown and Array I tests have confirmed that tar-

gets to be detected must be covered by at least two increments of a

sensor's resolution element. Figure 5 illustrates the locus of

points (a circle) on or within which an RPV must fly if a given num-

ber of resolution elements (or lines) are to be maintained on a mine.

Note that on a slope, the horizontal component of swath width is

narrower than on level ground. This effect is not serious as far as

search time is concerned in that even for very steep gradients, e.g.,

60%, the horizontal component is still over 85% of the width on level

ground (Figure 6). The width change is negligible on less steep

slopes on which minefields can be expected.

The television camera presently planned for use on the RPV is to

have a capability to image three fields of view (FOVs). These are

2.7 , 7.20, and 20' diagonal FOVs respectively. It can be shown that

the swath width attainable is eaual to

2s = 2h tan 2dm sin Cos

where h = RPV altitude,

., half the field of view,

n = the number of resolution lines desired on a target,

m = the total number of resolution lines

a = the mine diameter

For small 6, cos 6 is approximately one and sin 6 is approximately

6. The eauation may be simplified to

2s .d In

The swath width is independent of the FOV, directly proportional to

the number of lines in the television system and inversely propor-

tional to the number of resolution lines desired on the target. The

10


Locus of Points on Which Sensor Will Meet

Resolution Requirement

ASensor

Requirement is Met

Local

Ground Surface

Sensor Field Horizontalof View Component of/Swath Width

Mine

Figure 5. Geometry for Determining HorizontalComponent of Swath Width on a Slope

II

LERIM RADAR AND OPTICS DIVISION

1.0

--

= 0.9

0

0.

0

0 .

0 10 20 30 40 50 60Gradient (Percent)

Figure 6. Effect of Gradient on Swath Width

12

J-LIIM RADAR AND OPTICS DIVISION

swath width and the num-er of lines on a mine for a 3 1.0 line

system is illustrated in Figure 7 for the three FOVs. The

nominal swath width is approximately 70 m for two lines on a mine.

For a given FOV, the swath width becomes narrower as RPV altitude is

reduced (Figure 7). Simultaneously, the number of lines on a mine

increases.

Note that the narrowest FOV permits one to fly higher than the

wider FOVs. This is advantageous from the standpoint of maintaining

communications and from the standpoint of lessening mine obscuration

by vegetation. With a 2.7* field of view, the requirement for two

lines cn a mine limits maximum altitude above ground to approximately

1860 m. On the other hand, limitations due to cloud ceilings in-

crease with increasing sensor altitude.

The individual TV sensor elements integrate target/background

signal from frame to frame. Since RPV motion during the frame inter-

val (nominally about I m) exceeds the dimension of the individual

mine (0.3 m), ability to discern minefields is adversely affected.

Dependent on design approach chosen, this situation may also occur

for the forward-looking infrared system (FLIR). This effect and ap-

proaches to minimize it are discussed in more detail under RPV

characteristics.

Vidicon tubes with glass windows have a spectral response char-

acteristic whose peaks occur between 0.4 to 0.5 um or in the blue to

green oortion of the spectrum. The response is lown to about half

the maximum in the yellow portion of the spectrum and is not more

than 10% in the near infrared. In contrast, the human eye's response

peaks in the yellow portion of the spectrum. If ouartz windows are

used in the vidicons, their useful sensitivity can he extended into

the ultraviolet region. Silicon vidicons have broad high reponse

*Minimum reouirement of EIA Standard FS330, dated November 1966.

13


2000

2.70

1600

1200

-

4-)

400

02 °

0 20 40 60 80 100Swath Uidth (m)

mU ahIl I i I I I I

16 8 4 2Number of Lines on a Mine

Figure 7. Diagonal Field of View Versus Altitude and

Swath Width

Mine Diameter = 0.3 m

14

LLRIM RADAR AND OPTICS DIVISION

from about 0.4 to 1.0 pm [51. The response characteristics of these

several types of vidicons Should be compared to the spectral reflec-

tance characteristics of mines and backgrounds to determine if any

of these tube types offer an advantage over the others in detecting

surface laid mines.

One of two developmental FLIRs is to be chosen for eventual use

with the RPV. The specifications for either of these two units are

not yet available to ERIM. Conseouently, for the purposes of this

report, a FLIR system is postulated. This system is able to point

straight down, have the same diagonal FOVs as the television sensor,

namely, 20', 7.2, and 2.7' with an aspect ratio of 4 to 3, and to

have 0.10 mraa resolution in the vertical dimension of the 2.7' FOV.

This is tantamount to having a linear array of 280 detectors in the

vertical dimension with sweep in the horizontal dimension. The reso-

lution in the horizontal dimension is assumed to be the same as in

the vertical dimension. Since the number of detectors is fixed, the

resolution aecreases as the FOV increases.

. Eauations similar to those used for calculating the television

sensor altitude and swath width for a minimum of two lines on a mine

can be used to calculate the same auantities for the FLIR. These

values along with the resolution capability are listed in Table 1.

As for the television case, swath width remains essentially invariant

because the resolution decreases as the FOV increases. Similarly,

sensor altitude can be increased as the FOV increases. Again as for

the television case, in good weather, the narrowest FOV should be

used in order to minimize line of sight obscuration both for the sen-

sor and the data lirk.

It is of interest to note that the swath width for the postulated

FLIR is only 0.8 the swath width for the television system. This is

so because the FLIR has a resolution which is 25 percent poorer than

the television system. For the 2.7' FOV for both systems the

resolution is 0.1 mrad for the FLIR and 0.08 mraa for the television

15


TABl E 1FLIR ALTITUDE AND SWATH WIDTH

Diagonal FOV Resolution Sensor Altitude Swath Width(degrees) (mraa) (meters) (meters)

20 0.75 197 557.2 0.27 556 56

2.7 0.10 1685 95

16

L-RIM RADAR AND OPTICS DIVISION

system. If a resolution of 0.08 mrao is assumed for the FLIR with

353 detectors in place of 280 detectors for the 0.1 mrad system, both

the FLIR and television systems would have a swath width of 70 m.

17

M'RIM RADAR AND OPTICS DIVISION

5

OBSCURATIONAL FACTORS

The major obscuration factors for the RPV mission payload system

affecting sensory access are weather, terrain, vegetation and atmo-

spheric attenuation.

5.1 WEATHER

Figure 8 illustrates the percentage of time cloud ceilings are

below a given altitude in two areas of West Germany. At 1000 m al-

titude, cloud cover can be expected about 50% of the time at Bay-

reuth and 40% at Dusseldorf [6]. This suggests the use of the wider

fielas of view together with flight at the corresponding lower alti-

tudes when cloud ceilings obscure visibility at the higher altitudes.

5.2 TERRAIN

The effect of sloping terrain was illustrated in Figures 5 and A

and discussed in the accompanying text. Generally anti-vehicular

minefielrs are to be expected in trafficable areas (slopes of 3C' or

less). ConseQuently, reduction in swath width will be minimal.

Since the viewing angle of the RPV mission payload sensors can be

adjusted over the lower hemisphere, a partial compensation for ef-

fects of terrain slope on sensor performance is available to the RPV

operator or sensor operator.

5.3 VEGETATION

The effect of vegetation in obscuring sensory access to mines

can be important. The geometry of vegetational obscuration of a mine

is shown in Figure 9. The mine is assumed to te or a flat terrain.

The sensor carrying air vehicle is assumed to be flying in a straight

line with a level attitude and the sensor is assumed to he

18


1500 - -

Cloudy --- Clear.-4

Days Days

FoggyDays

Dusseldorf /

Bayeut

/

00 20 46080 100

Frequency of Ceilings Below a Given Altitude (Percent)

Figure 8. Cloud Ceilings Below a Given Altitude

Dusseldorf, Zone 5(a); Bayreuth, Zone 7(c).

19

Y-ERIM RADAR AND OPTICS DIVISION

Sensor

hnMine R

ha

hr

d a

Figure 9. Sensor, Mine and Vegetation Geometry

20

L I RADAR AND OPTICS DIVISION

stabilized. The vegetation is assumed to be sufficiently dense as

to completely obscure a mine if interposed between the mine and the

sensor. This assumption for vegetation density should lead to con-

servative results since foliage density will vary considerably ac-

cording to the types of plants and seasonal changes. The numbers

arrived at should be viewed as boundary values useful in choosing

operational conditions of flight.

Vegetation effects or permissible flight paths can be determined

by calculating the limitina half scan angle 6L from the

vegetation-mine geometry. The line of sight is assumed to be

completely blocked by vegetation. The angle can be expressed by

OL = tan -1 [(z1 d + a)/(h v - h m)]

where 2 is that fraction of the mine diameter, d, obscured hy the

vegetation and a is the projection of the distance measured from the

mine edge to the point on the plant which just blocks the line of

sight, h is the plant height and h is the mine height. If aV m"

is negative, a portion of the plant overhangs the mine (Figure

10(a)). For positive a, there is no overhang (Figure 10(h)). Which

situation exists depends on plant type and number of plants in a

mine's vicinity. The fraction 2 can takeP on any value between 0 and

1. If zero, no overhang can exist and a cannot take on negative

values, if one, overhang is complete (or the vegetation is infi-

nitely tall, an impossible condition) and a is eoual to -d. For any

other value of Z between 0 and 1, a can be any positive value or any

negative value which is not less than -e. For example, if Z is 0.5,

the eauation for 6, is

L t an + a)/(hv - hm)]

d-- a <

21


(a) a is negative and the plant overhangs the mine

I

!jind

,

h

L

I7 ad

(b) a is positive and there is spacing

between plant

and mineFigure o. Geometry for the Overhang Case

22

SRIM RADAR AND OPTICS DIVISION

Specific cases of vegetation effects are plotted in Figure 11

for three different values of resolution and for z = O. Spacing a

between vegetation and mine is 0.05 m (2 inches). The vegetation

limiting radials apply to all three resolution circles. Vegetation

with a height of one ft (0.3 m) limits achievable swath width to ap-

proximately two thirds of the maximum achievable under ideal condi-

tions. This figure clearly illustrates that sensors should be flown

somewhere in the upper half of the permissible locus, preferably as

close to mid-altitude as possible (with respect to the theoretical

maximum) in order to maximize swath width. The effect of variations

in spacing between mine and vegetation is illustrated in Figures 12

and 13. Altitudes and swath widths in Figure 12 are normalized with

respect to the locus circle diameter given by d/nA6. If the spacino

between mine and vegetation is reasonably large, as in cases c and

d, the achievable swath width is respectable even for vegetation as

tall as 0.5 to 0.6 m. These figures underline the importance of at

least estimating the nature of plant cover at suspected minefield

locations so that reasonable missions can be flown.

In many instances, plants will overhano a mine so that only por-

tions of that mine can be seen. In terms of the limiting anale

eauation, a takes on negative values. How much of a mine is observ-

able from a given aspect angle is a function of many variables in-

cludino plant type, spacing, growth season, etc. Any meaninqful data

must be gathered in the field and the data treated on a statistical

basis. Nevertheless, it is instructive to calculate the effects of

overhang on the scanner FOV, altitude, and swath width using the

geometry of Figure lOa. That fraction of the mine diameter which is

not ooservable is labeled zd. Note that that portion of the mine

which is observable may include a portion which is beneath vegetation

overhang on the side opposite the viewing direction. This may not

be a valid assumption for passive sensors but the conclusions which

can be drawn from the assumed model are sufficiently realistic to

23

RADAR AND OPTICS DIVISION

wm

1600-

1400 0. 60 m

1200 0 00 6

800o~0.i1 mr

C SensornResolutio

") 600

e t 0Vegetation4 Height" 4000.15 m

200

0 200 400 600 800

Half Swath Width (Mleters)

Figure 11. Effects of Vegetation Height and SensorResolution on Sensor Altinude and SwathWidth. Spacing Between Nine andVegetation , 0.05 m.

24

LERIM RADAR AND OPTICS DIVISION

1.01 0.60 0.01.0 1.2 0.9 . .0.0 .60.,

0.90 .2

1.2 0.30.20

0. Z5

- 0.5

,2 0.5

- 0.20

0. 15 cm

D. 15 m

01 T _ _.

0 0.5 0 0.5Half Swath Width Half Swath width

a. a -0.05 a b. a -0.10 a

1.0. 181.209 1.0. 1.8 1.2 .060 .0.0 0.6

0.40 0.5

0.4Ii0.30 0.35

-0.5 0.5.0.25 0.301'

0.25

0.20500.20

Vegetation* 0. 15 a Height 0. 15 m

C C0 0.5 0 0.5

Half Swiath Width Half Sw~ath WidGth

c. a -0.15 w d. a .0.20 .0

Figure 12. Vegetation Effects on Altitude and Swath Width asa Function of "a"

Altitudes and swath widths are normalized with respectto d/nho. "a" is the spacing between mine side andvegetation.

25

L RIM RADAR AND OPTICS DIVISION

800Tr * r- T

600 ____

.6J

~n200 00

0

Vegetation Height (Meters)

Figure 13. Vegetation Height and Spacing Effects on Swath Width

a is the distance between mine and vegetation. Twolines on the mine and sensor resolution of 0.25 mrad.Scan angles greater than 450 result in swath widthsnarrower than the maximum width (part of curves to theleft of the peaks) and scan angles less than 450 resultagain in swath width narrower than the maximum width(part of curves to the right of the peaks).

26

RIMo RADAR AND OPTICS DIVISION

delineate reasonable operational limits. Only field data can provide

more realistic information.

Figure 14 illustrates how overhang or spacing between vegetation

and a mine affect the limiting scan angle. If vegetation overhangs

a mine, the scan angle is limited to small values. For vegetation

even as short as 0.3 m, the useful half scan angle is less than 1O

deg. if either one auarter (z = 0.75) or three ouarters (i = 0.25)

of the mine diameter is to be observable. For the former case, the

overhang car be as muc as 0.225 m. In the latter case, where more

of the mine must be seen, the overhang can be maximum of 0.075 m.

In both these cases, the limitina half scan angle is zero. As ex-

pected, the limiting scan angle increases as overhang decreases and

spacing between mine and vegetation increases. Figure 14b illus-

trates an intermediate case in which half a mine (9z = 0.5d) must be

observable. It is clear from these figures that overhang severely

bounds the scan angles over which mines can be detected; hence, swath

widths will also be decreased substantially with swath width given hv

2 (1 -)d sin 20n +

for 6 less than 0L"

5.4 ATMOSPHERIC OBSCURATION

Scatterina and absorption are two mechanisms which affect the

transfer of radiation in the Earth's atmosphere. Both molecules and

aerosols are involved in these processes. High concentrations of

aerosols and gasses close to the ground can be expected on a battle-

field, concentrations caused by dust churned up by vehicles, exhaust

gasses, gun smoke, smoke intentionally emitted for screening pur-

poses, etc.

How environmental, seasonal and diurnal conditions affect trans-

mittance has been studied and modeled extensively [4]. Many

27

S-[RIM RADAR AND OPTICS DIVISION

3 80 ; - 0.75 d

"0 /a - 0. 20 m.e- 0.10

0.0;60 -0.10

C 50 € 5 ;.- 0.35 ml

4 0.15

0.05q- 30 -. o

S20

" 01

U

= 2

.- 0 0.3 0.6 0.9 1.2 1.5 1.8-J

Vegetation Height, hv (m)

a. One quarter Q7 - 0.25 d) and three quarters ( - 0.75 d)9 f a mine not observable

a,

- 60

' 50

4

a 0.20m30

in

o 0

-J 0 0.3 0.6 0.9 1. 2 1.5 :.8V'egetation Height, h,¢ m.)

b. one-Ralf (z - 0.5 d) of a mine not obserable

Figure 14. Effect of Vegetation Spacing on LimitingScan Angle.

Negative values of a refer to overhang.

28


measurements have been made as well, particularly along horizontal

paths. Apparently, little data have been gathered on transmissivity

characteristics along vertical paths, particularly at low altitudes.

What data exists indicates that high extinction coefficients can be

expected at those altitudes at which mine and minefield detection

sensors would be flown. These coefficients vary widely depending on

the weather ana other environmental conditions.

How atmospheric transmissivity affects particular minefield de-

tection sensors should he modeled and valiaatea bv experimental

results.

29


6RPV CHARACTERISTICS

The major characteristics of the RPV which affect minefield de-

tection performance are delineated and discussed herein. Endurance;

range; altitude limits; minimum, cruising and maximum speeds; degree

of stabilization available for sensors; payload; vulnerability; sor-

tie rate and fielo of unobstructed view available to the sensor pack-

age are among the important RPV parameters affecting minefield de-

tection performance.

The range measurements from FESA associated with minefield de-

tection are as illustrated in Figure 1. The RPV range capabilities

substantially exceed these reauirements for a typical brigade or di-

vision front (the divisional RPV allocation consists of four

sections).

Similarly RPV endurance is ouite adeauate for detailed examina-

tion of designated areas and for conducting general search patterns

in the areas where enemy doctrine indicates minefields will he used.

This subject is discussed in more detail in Section 11.

The RPV service ceiling of at least 3600 meters greatly exceeds

the maximum altitude at which current or planned sensors can resolve

Soviet mines and minefields. Further, reference to Figure P indi-

cates the general desirability of RPV flight at altitudes consider-

ably lower than 3600 m in order to minimize effects of sensor obscu-

ration by clouds.

The preliminary examination has been made of the effects of PPV

speed on sensor and man/machine interface performance. The magnitude

and range of RPV speed, 90 km/h minimum, 180 km/h maximum and 120

km/h typical cruise, together with target resolution and look angle

reauirements impose operatino mode restraints on the TV sensor and

they may impose similar restraints on the FLIR sensor dependent on

30

.r


particular FLIR design. Assuming spatially stabilized sensor viewing

from a near-nadir position with a frame rate of 30 per sec, then RPV

motion represents a displacement potentially varyino from 0.83 m per

frame to 1.67 m per frame. Since the TV sensor elements integrate

signals from frame to frame the signal from the mine (0.3 m diameter)

will be integrated with signal from adjacent background (0.83 to 1.67

m in length). To avoid this effect the TV sensor can be out in the

correlation tracker mode and reset periodically in accordance with

RPV speed so that complete coverage in the flight direction is ob-

tained. Contacts have Deen made with the RPV mission payload sub-

contractor and his preliminary assessmente indicate the feasibility

of this "snapshot" mode of operation. This "snapshot" mode can alsobe used with a FLIR. The effect of continuous motion as dmscribed

or a "snapshot" presentation on the ability of the RPV display ope-

rator to detect Soviet mines or minefields is uncertain at present.

It is recommended that resolution of this uncertainty be a priority

item for future effort.

The degree of stabilization of the sensor packade in both point-

ing and tracking mode appears adeouate when considered in terms of

its effect on resolution of the individual mine. If the "snapshot"

mode is used, the settling time of the sensor servos from snapshot

to snapshot appears adeouate in a preliminary assessment. The PPV

has considerable growth potential in payload weight and space avail-

able in the event changes specifically oriented towards minefield

detection are deemed desirable.

The survivability of tre RPV system as currently corfioured ap-

pears to be reasonably well established and compatible with the mine-

field detection mission. Inasmuch as the RPV in minefield detection

missions is not expected to be reauired to penetrate more than ap-

proximately 35 km beyond FEBA (forward edge of battle area) for

scenarios 1 and 4, only limited air defenses are expected to be

employed against it (see Figure 1) for these scenarios. A lesser expo-

sure to air defense is expected for scenarios 2 and 3.

31

4:

EiRIM RADAR AND OPTICS DIVISION

The RPV sortie rate of three per twelve hour period per section

together with the endurance and speed capability of the RPV appears

compatible with the response times needed in conrection with the

Soviet minefield scenarios.

The large range of viewing angles made possible tv the PPV hemi-

spherical arrangement for sensor location allows flexibility for RPV

maneuvers. The gimbal arrangement is such that viewinc from nadir

is not recommended. It is possible to have viewing angles 10' to

l5' off nadir with satisfactory gimhal servo performance. This ar-

rangement appears acceptable for minefield detection purposes if

there is sparse, short, or no vegetation. If veaetation is 0.3 m or

taller, scan angles will be limited to values less than 10' to 15'

off nadir so that some provision must be made to stabilize the sensor

against RPV roll.

32

-E'RIM RADAR AND OPTICS DIVISION

7DATA LINK CHARACTERISTICS

The current RPV missions reaulre that a microwave around based

data link be used to keep track of RPV position, to send flight com-

mands to the aircraft and to command sensor modes of use. Sensorcollected data and RPV systems status is transmitted from the air-craft to the ground. The data link system is to have a high deqree

of immunity to countermeasures. The same overall reauirements hold

when RPVs are to be used for mine ana minefield detection purposes

although it is not yet clear whether the data link as planned will

aaeauately fulfill the reouirements of minefield detection missions.

The Modular Integrated Command ana Navigation System (MICNS) is

the microwave data lihk system slated for use with the RPV system.

A tracking antenna is mounted on a remote ground terminal and main-

tains track of the RPV as long as there is a dirEct line of sight.

Navigational commands and sensor commands are periodically relayed

to the aircraft. RPV status is sent to the around on the down links.

Data rate is low, and narrow band signals can be used on these links.

When search is in progress or a target has been acauired, video is

also transmitted from the RPV to the ground. Conseauently, the down-

link bandwidth must be wide to accommodate the video signal from the

TV sensor.

Low altitude RPV operation has the unfortunate effect of forcino

the ground based data link antenna to track at low elevation angles.

The effect is unfortunate because multipath reflection, i.e., the

reflection of microwave signals from the ground near the antenna

causes the amplitude and phase of the signal received at the trackino

antenna to vary significantly from the amplitude and phase of the

direct signal. Multipath reflection from the around surroundina the

antenna is particularly bad at low elevation tracking angles. Signal

magnitude can he reduced essentially to below noise level or

33

.-

L-RIM RADAR AND OPTICS DIVISION

increased theoretically to a maximum of twice the direct signal

value. Tracking errors of a degree or more are not uncommon and can

occur with either amplitude or phase controlled trackino systems.

It is expected that the low angle tracking problem is being addressed

during the course of MICNS development since other RPV missions be-

sides the minefield detection mission are likely to share this prob-

lem. The Problem is a common one and has received considerable at-

tention over the years.

Another unfortunate effect of the low altitude requirement is

terrain masking of the line of sight (LOS). Table 2 lists minimum

altitude for electronic line of sight as a function of ranae from

the remote ground terminal (RGT) of the data link system. In situa-

tions where terrain maskina is severe or where the Soviet minefields

are located in the more distant portions of scenario I it may be ad-

vantageous to use a data link relay. This relay could be mounted in

an RPV which hovers near the RPV ground control station at an alti-

tude sufficient to insure a direct line of sight to the RPV whose

mission is minefield detection.

The television system's video bandwidth is assumed to be the same

as required for commercial television. Allowing some bandwidth for

control signals, this bandwidth is 6 MHz. The important factor is

whether or not resolution needed for minefield detection is degraded

within the data link system. A bandwidth compression technioue or

signal coding technique used in data link transmission may be de-

signed to discard some of the information oathered by the sensor de-

pending on the target sizes and on the resolution required for an

operator's display. Whether or not such degradation sufficient to

affect minefield detection occurs in the MICNS should be investigated

as a matter of priority. Minefield imagery has been provided to

MERADCOM for retransmittal to the data link contractor for an initial

determination as to whether data link characteristics will affect

minefield detection performance.

34


TABLE 2MINIMUM ALTITUDE IN METERS FOR ELECTRONIC LINE OF SIGHT

RANGE FROM RGT (REMOTE GROUND TERMINAL) IN km

Si te-to-Mask(Mils) 1 km 5 km 10 km 20 km 40 km

5 5 25 50 100 200

10 10 50 100 200 400

20 20 100 200 400 POO

30 30 150 300 600 1200

100 100 500 1000 2000 4000

200 200 1000 2000 4000 8000

35

--RIM RADAR AND OPTICS DIVISION

8MAN/MACHINE INTERFACE

As presently organized ana manned, the RPV section has a sensor

operator and RPV operator who view the TV type sensor display and

control the sensor view angle, field of view, stabilization modes and

flight modes. Normally for target acauisition the sensors look for-

ward or to the side and depression angles are generally substantially

less than one radian. For minefield detection, with its emphasis on

resolution ani sensory access, it is desirable for the sensor view

angle to be near nadir. When the sensor is near nadir the imagery

displayed appears to move essentially in accordance with the PPV

ground track. This situation leads to several auestions - (1) Are

the sensors effective in this mode and (2) Assuming sensor operation

is satisfactory, can the human RPV or sensor operator effectively

detect mines or minefielos?

The first auestion has been discussed in connection with the ef-

fect of RPV speed on sensor and man/machine performance in Section

6. Two "asic sensor modes are suggested, continuous motion mode

and "snapshot" mode. As currently configured the TV camera imagery

fuality will be seriously degraded due to relative motion of the

sensor with respect to the ground in the continuous mode but is ex-

pected to be of satisfactory auality for the "snapshot" mode. Full

FLIR information is not available at this time. It is our current

understandina that the FLIR also will be satisfactory in the "snap-

shot" mode and may be satisfactory in the continuous mode, continoent

upon the particular design chosen.

The effect of these modes at the man/machine interface on the

ability of the RPV or sensor operator to detect Soviet mines or mine-

fields is uncertain at present. Experiments usina actual minefield

imagery in a simulated RPV environment to ascertain and define RPV

or sensor operator capability to detect Soviet mines and minefielis

nave been designed and proposed to MERADCOM for future effort.

36

-RIM RADAR AND OPTICS DIVISION

9

COMMAND, CONTROL AND COMMUNICATIONS

The RPV platoon is organic to the target acquisition battery of

the division artillery and functions under the staff supervision of

the division artillery S-3. The platoon will consist of a head-

quarters section and four RPV sections. Each RPV section will nomi-

nally have five air vehicles, a ground control station and a launch

and recovery capability. Normally, one RPV section will be placed

in support of each committed maneuver brigade (i.e., supportea unit)

and one in general support of the division.

The platoon leader commands those sections retained under divi-

sion artillery control. In addition to acting as the advisor on RPV

employment to the division artillery commander, he is responsible

for ensuring that the operational sections are trained, and monitors

logistical support (to include organizational maintenance) and ad-

ministrative support.

The section leader commands the individual operatiorfal section.

He coordinates operations and training and logistical and admini-

strative support with the platoon leader and the controlline unit

commander/staff.

The platoon leader retains control of the operational sections

until they deploy in support of a divisional unit. Upon deployment,

operational control of a section is assumed by tip supported unit

commander.

The RPV section leader advises the supported unit commander and

his staff on RPV technical aspects to include air vehicle and sensor

capabilities, weather contingencies and suitability of flioht routes.

When the RPV section is supporting a maneuver brigade it will

normally ooerate in the Brigade Radio Intelligence Net, the Field

Artillery Battalion Command Radio Net, and the DS Field Artillery

Battalion Operations/Fire Radio Net. When the tactical situation

37

2RIM RADAR AND OPTICS DIVISION

and distances permit, wire communications will be established to the

direct support field artillery battalion's switchboard, and TACFIRE

set, or to the maneuver brigade switchboard.

When the RPV section is supporting the division the communica-

tions reauirements for the Division Support Section are similar to

those cited for the maneuver brigade. Wire is the preferred mode of

communications when distance and the tactical situation permit its

installation. Communications will be established as directed by di-

vision artillery. The RPV section will normally operate in the Di-

vision Intelligence Net, the Division Artillery Command Net and the

Division Artillery Target Acouisition Battery Command/Intelligence

Net.

Since the RPV section supportina the maneuver brigade is directlv

tied to it organizationally, in command structure and through its

communication nets; its responsiveness will be high and its response

time low.

38


10FLIGHT REGIMES

This section presents a consolidation of various factors limiting

the flight regimes where minefield detection is possible. Consider-

inq vertical flight regimes, sensor resolution at the narrowest field

of view (2.70) limits maximum altitude above ground to approximately

1860 m (see Sensor Characteristics). A minimum altitude limit is

imposed by the electronic line-of-sight requirement of the data link

(see Table 2). Between these extremes, the weather may impose addi-

tional limitations (see Figure 8).

Analysis results indicate that infrared scanners, FLIRS, and

television cameras must be operated at low altitudes if these sensors

are to be able to detect mines and minefields. The chief driver fnr

this requirement is the prevalence of cloud cover, particularly if

the area of concern is West Germany. On clear days or in areas where

cloud cover is at high altitudes or seldom occurs, the driving func-

tion limiting flight altitude is sensor resolution capability. This

latter altitude limit is generally higher than the limits imposed by

cloud cover over Germany. Figure 15 illustrates cloud ceiling

values over Bayreuth as well as the maximum altitude at which a tele-

vision camera can be flown so that there are at least two scan lines

across a mine. This figure clearly shows thdt the wide FOV must beused most of the time if the sensor is to be below the cloud cover.

The effect of several typical elevation tracking angles and obstacle

clearance angles (mask) which determine electronic line of sight are

also shown in Figure 15.

Point and areal coveraqe typically is within RPV endurance limi-tations and is separately discussed in Section 11.

Tracker limitations can also impose restrictions on permissible

flight regimes. Assume, for example, that the RGT (remote ground

39

LERIMRADAR AND OPTICS DIVISION

1600 _

-2.7 0 FOV

1400

3 0

1200

1000

2 50

CU

600OC

0

thre FOOs C401


terminal) is located reasonably near the Ground Control Station as in

Figure 1. When searching for hasty minefield blocking withdrawal

(Scenario 3), tracking angle can range from as low as 1.50 when the

minefield is at one side of the brigade front and the tracker at the other

(approximately a 10 km range) to directly overhead. If the system isnot designed to track an RPV which is directly overhead, there will be

a circular area surrounding the remote ground terminal in which it willnot be possible to search for minefields. The radius of this area is

given by the RPV altitude divided by the tangent of the maximum tracker

elevation angle. If this angle is 600 and the RPV altitude is 1500 m,the circle radius is 866 m; at an altitude of 250 m, the radius is 144 m.

Minefields in Scenarios 1 and 4 will be located approximately 5 to

45 km from the tracker. At 5 kmn, elevation tracking angles will seldom

be below 30, even if the RPV is only at 250 m altitude (Figure 15).

Under such circumstances, the RPV will be below cloud ceilings about 90%

of the time. If a minefield is 45 Wm from the tracker and the RPV

is at 250 m, the tracker elevation angle will be only Q*30, Any obstaclein between the tracker and the minefield which exceeds the Q.3* line on

Figure 15 will block the LOS. If weather conditions permit, it is clearly

desirable to fly at the higher altitudes so that LOS blockage cannotI occur. (Atmospheric refraction will cause the propagation paths orobstacles clearance lines to be lifted slightly above the lines which

are plotted in Figure 16, but the effect at these short ranges is small.)

Another conclusion which may be drawn is that the remote ground terminal

should be placed as high as possible on the local terrain.

41

LMRIM RADAR AND OPTICS DIVISION

U__ S- 44

Ln wa4

4o(_ _ _ _ _ _ _ _ _ _ _ _ aI

2 D

A 7

4, 42

-ERM RADAR AND OPTICS DIVISION

11

POINT AND AREAL COVERAGE

The RPV system has capability for both target acouisition/

designation and areal reconnaissance [1]. Generally these capabili-

ties can te associated with point and areal ccveraao. Both coveraaps

have applicability in connection with minefield detection. Response

times for point coverage can be represented as the time rpouired to

launch and fly the RPV to the point where minefield detection cover-

age is desired. Assumina an air vehicle is availahle ready for

launch for such a mission then response time can be closely approxi-

mated by the RPV flight time to the desireo point. For the scenarios

of interest for minefield detection and using the minefielo relation-

ships with respect to the FEBA and the RPV around control statior

location shown in Figure 1 flight time typically is 40 min for

Scenario 1. For Scenario 2, it is 12 min and for Scenario 3 it is 26

min. Scenario 4 ranges from 26 min to 3 hrs dependent on depth of

coverage.

Fqr areal coverage (reconnaissance) we may consider three aeneral

categories of missions; area reconnaissance, specific reconnaissance

and route reconnaissance. Minefield detection may be associated with

each of these categories. Within the limitations of our minefielo

detection scenarios, the first category, area reconnaissance, is the

broadest of the three categories. tn RPV section might typically

provide area reconnaissance to detect Soviet minefields over a bri-

gae front of 6 to 10 km to a depth of 4 km beyond FEBA. Assuming a

swath width, of 70 m brigade minefield detection area coverage elapsed

time could range from 11 min to 6.5 h. Such coverage could typically

be reouireo in connection with Scenario d. This particular scenario

imposes much less stringent search time constraints than the other

scenarios. Figure 16 shows typical search areas for the Soviet mine-

field scenarios. It also presents typical minefield search times

for thesP scenarios. These typical search times are based cr an PPV

43

L-'RIM RADAR AND OPTICS DIVISION

ground speed of 140 km/h and search conducted in a direction normal

to the expected orientation of the minefield. These times include

typical flight times in the search area. It should be noted that

the typical search times are generally quite modest when compared

to RPV endurance.

Scenarios I and 2 could be considered as typical examples where

specific reconnaissance is required. Search time values for these

scenarios can range from 12 min to 1.5 h of RPV fliaht for Scenario

2 and from 40 min to 13 h for Scenario 1.

Scenario 3 is representative of route reconnaissance. Search

time values for this scenario can range from a.0 min to 21.0 min.

The range of search times presented represent variation of RPV

flight time required for complete coverage from the extreme condition

wrere too RPV speed is used and search paths are conducted in the

most favorable orientation to the other extreme where lowest RPV

soeea is used and search paths are conlucted in the least favorahle

orientation. All search times include appropriate values for the

fliqht time required to reach the search area from the RPV launch

site. It should be noted that the tracker can impose limitations on

coverage. This subject is discussed in Section 7.

44

.1L

-[RIM RADAR AND OPTICS DIVISION

12POSSIBLE NEXT GENERATION SENSOR SYSTEM

An examination and assessment of the current RPV TV sensor system

and the planned RPV FLIR sensor system from the standpoint of mine-

field detection reveals the possibility of substantial improvement.

In general these improvements would not degrade performance for other

missions and in some cases would substantially improve capabilitv

for them.

From an operational standpoint it would be highly desirable to

improve the percentage of time wherein the RPV minefield detection

system could be utilized. Further it is highly important to reduce

the time during which the RPV is in flight over areas where its sur-

vivability is at risk. Finally, it would be highly desirable for

the RPV minefield detection system to have a high probability of de-

tection and a low probability of false alarm.

Considering these important operational factors, there are sev-

eral technical approaches which are available to alleviate current

limitations.

To increase the percentage of time when RPV mine detection capa-

bility is useful there are several attractive approaches. Foremost

of these is the currently planned addition of a FLIR capability to

the present RPV system. This passive IR sensor would add a nighttime

capability to the current day capability of the TV sensor. The por-

tion of time when sufficient thermal contrast exists for passive IR

minefield detection is discussed in Section 3.

Although the addition of a passive infrared sensor capability to

the PPV sensor package improves the nercent of time useful compared

to a TV system because the passive system can sometimes be used at

night, the passive IR sensor is still limited to perioms when suffi-

cient thermal contrast exists between the mines and backarouno. Re-

cent investioations at ERIM have established that the PY-60 and TM-11F

45

/

'ERIM RADAR AND OPTICS DIVISION

Soviet mines give strong specular returns when illuminated hy a 10.6

pm laser beam [7]. These returns are relatively independent of the

thermal conditions at the mine and its immediate surroundinq. The

beam of the specular return is but a few deorees wide and accordingly

the return is sensitive to the angle of repose of the mine with re-

spect to the illumination beam. Thus mine detectability is a func-

tion of terrain irregularity. It should he noten that sianal-to-

clutter ratios of 102 or more are not unusual for such a system

and that detection of all individual mines is not a reauirement for

detection of a minefield. Further the strona sional-to-clutter ratio

lends itself to automated operator assist or target recognition

schemes. Based on these consinerations active IR or a comhination

of passive and active IR seems worthy of detailed exploration and

demonstration as a means for improving the percentaae of time when

the minefield detection system can be utilized.

Another possibility for improving percentage of time useful 'r

minefield detection is to operate the RPV at lower altitude regimes

where cloud obscuration effects are diminished. This effect is viv-

idly illustrated by Figure 8. This approach has limitations such as

performance reouirements of the data link. The data link reoLuires a

clear electronic line of sight to the RPV. Fiaure 15 lists the mini-mum altitude for electronic line-of-sight as a runction of the anqle

between the RGT site and the mask; and the range of the RPV from the

remote around terminal. It is apparent that data link performance

severely constrains RPV flight at lower altitudes and that consider-

able attention should be paid to site selection for the RGT to mini-

mize this constraint.

Another way to improve operational effectiveness is to decrease

the exposure time during which the RPV is in flight over areas where

its survivability is at risk by reducina the minefield search time.

A possible means for realizing reduced search time is the use of a

wider swath width. The wider swath width in turn implies a hiaher

46

Y-ERIM RADAR AND OPTICS DIVISION

TV or FLIR data rate with its attendant reflections on the data link.

One possible solution to this difficulty would be the use of line

scanner techniques which would allow significantly lower data rates

than the TV or FLIR currently planned for the RPV. Another approach

would involve on-board preprocessing of sensor outputs to reduce ef-

fective data rates to a degree amenable to the data link without

significant degradation of essential minefield detection information.

Operational effectiveness can also be enhanced for minefield( de-tection systems by improving the probability of detection and rpduc-

ing the probability of false alarm. There are at least three means

for accomplishing this objective, all of which are applicable to the

RPV system. First, it is possible to decrease probability of false

alarm (PFA) through improvee resolution and sensitivity of the

sensor system. For the RPV TV and FLIR sensors improved resolution

while maintaining coverage implies higher data rates. Again line

scanner techniques or on-board preprocessing of the sensor data ap-

pear to be possible approaches to attainment of improved resolution.

Considering improvement of sensor sensitivity, minor improvements

may be expected but current sensors approach theoretical capability

limitations. Secondly, it is possible to achieve improved PD and

lowered PFA through the use of more distinctive target signatures.

As previously discussed, active IR mine signatures at 10.6 jm are

auite distirctive and offer possibility for lowerina of PFA It

should be noted that the probability of detection for this approach

may be rather low. However, there will be a high confidence asso-

ciated with mines detected using active IR at 10.6 um. Again, the

combination of active and passive IR appears to be complementary and

attractive for minefield detection. A third approach. to improve

PD ann lower PFA involves a more effective man/machine

interface. It appears possible to provide considerable assistance

to the sensor operators and the RPV operators in the detection of

minefields through various automatic enhancement techniques. For

47


example, all detections involvinq targets larger than an individualSoviet mine could be rejected; all detections having specified

spatial arrangements peculiar to Soviet minefields could be enhanced.Finally, it seems possible through extension of these technioues,that Soviet minefields could be recoanized automatically togetherwith initiation of search patterns intended to completely define and

precisely locate them.

48

W- odd

JERIM RADAR AND OPTICS DIVISION

13

FINDINGS AND RECOMMENDATIONS

13.1 GENERAL

Finnino 1. The RPV system, as presently confioured anm planned,

will have a significant and operationally useful capability to detect

Soviet minefields in the West German theater. The minefield detec-

tion capability of the RPV should be explored for other theaters of

interest. The RPV system, as presently configured, uses a television

sensor and consequently is limited to daytime use, perhaps on the

order of eight hours or less each day, particularly in winter. How-

ever, the RPV system does not restrict night use since the system is

designed to accommodate night launches and recovery. Acouisition of

a FLIR sensor as is already planned will enable the Army to increase

the usable operation time to nights as well as days. It is expectoo

that FLIRs can be used to detect Soviet mines and minefields since

the FLIR resolution capability will be similar to that of the tele-

vision system. The FOVs for the FLIR are assumed to be the same as

the television system.

Recommendation 1. Since the FLIR is currently under development

for the RPV application, the various FLIR approaches should be re-

viewed for compatibility and upgradino potential with respect to the

minefield detection mission.

13.2 MINES AND MINEFIELDS

Finding 2. Preliminary tests indicate sufficient thermal and

optical contrast can exist between mines and background that mine-

field detection is possible under prooer circumstances [8, 9].

Recommendation 2. Experiments and data acquisition efforts

should be designed and implemented to delineate ranqe and freouency

of occurrence of target/background contrast levels to be expected

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for current planned and potential sensor complements for the RPV.

These efforts should encompass a sufficient time span so that the

effects on contrast of seasonal and vegetational variations can be

appropriately assessed. The objective of this effort is to develop

an information base sufficient to determine the pprcentage of time

conditions exist at the minefield which would allow its detection.

The current effort to acauire mine and minefield data in a simulated

West German environment at array II and supplemental arrays in Oregon

shoula be continued. The appropriate portions of RPV Phase I and 2

of Plan III [10] should be implemented. In addition, consideration

should be given to developmert of target/backaround contrast data

for other theaters.

Findin2 3. Preliminary tests indicate that Soviet PM-60 and

TM.-46 mines give strong specular returns compared to background when

illuminated at 10.6 um. A similar but lesser effect exists at 1.06

um [7].

Recommenoation 3. Since the active IR depends on a different

signature effect, it offers potential for expanding the percent of

time conditions at the minefield exist which would allow its detec-

tion. It is recommended that this approach be investigated suffi-

cient to allow substantiated judgments to be made regarding its use

in conjunction with the RPV system. The effort delineated in New

Concepts, Subsection 1, Phase I of Plan III approoriate to the RPV

system should be initiated with this objective.

13.3 SENSORS

Finding 4. At least two increments of the sensors resolution

element must cover a mine in order for it to be detected. Both the

TV sensor and the planned FLIR sensor are capable of providing the

reauisite resolution under certain RPV flight regimes. Maximum swath

width of 70 m and RPV operating altitude of 1860 m for minefield de-

tection are limited by resolution capability of the sensors.

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-E:RIM RADAR AND OPTICS DIVISION

Recommendation 4. Possibilities for increasing sensor resolution

capabilities should be explored sufficient to provide a basis for

decision regarding the desirability of upgradinq sensor resolution.

This effort should include the focal plane array study suggested as

Phase 1, Task 1.6 of the Active IR effort. Since improved resolution

affects data rate with possible attendant reflections on the data

link design, the resolution study should consider these implications

and means for minimizing their effect. The use of line scanner tech-

niaues or onboard preprocessors, as suggested in Section 11, as a

means for allowing significantly lower data rates should be included

in the study.

Finding 5. With the TV sensor, minefield detection is limited

to conditions of favorable contrast during daylight hours. The use

of the planned FLIR will generally allow more favorable mine/ back-

ground contrast and both day and night operation. Other sensor ap-

proaches and combinations of sensors offer the possibility of further

improvement in percent of time the sensor system is useful for mine-

field oetection.

Recommendation 5. Active TV should be explored as a means for

extending percent of time useful for the TV sensor. The planned FLIR

approaches considered for the RPV should be scrutinized ir detail to

ascertain their suitability for the minefield detection mission. If

modifications are found to be necessary, they should be made as early

as possible in tne development cycle. Alternative sensor approaches

and combinations of sensors should be explored in detail with the

objective of improving percent of time useful and probability of de-

tection and decreasing probability of false alarm. To implement this

recommendation, the appropriate portions of RPV Phases 1 and 2 ef-

fort, together with active IR effort of Plan I1 [10], should he

imp lemen ted.

Finding 6. RPV flight motion along the ground track will tend

to degrade TV imagery and may degrade FLIR imagery dependent on

51


aesign approach chosen. This effect increases as viewing anales ap-

proach nadir. RPV flight motion may also affect man/machine inter-

face performance inasmuch as it may degrade sensor operator ability

to detect minefields.

Recommendation 6. Effects of PPV motion along the flight path

on sensor imagery and minefield detection performance should be thor-

oughly investigated together with the development of approaches to

reduce effects of RPV flight motion to acceptable levels. As a mini-

mum, the "snapshot" mode discussed in Section 4 should be thoroughly

investigated and demonstrated. Ancillary effects such as effect on

RPV sensor operator ability to detect mines shoul' also be mame a

part of this investigation. The recommended effort is generally de-

scribed in the appropriate portions of RPV Phase 1, 2 and 3 effort

of Plan I1.

13.4 OBSCURATIONAL FACTORS

Finding 7. The major obscuration factors for the PPV mission

payload system affecting sensory access are weather, terrain, vege-

tation and atmospheric attenuation. These factors are characteristic

of and generally unique to the theater of operations.

Recommendation 7. The ongoing and planned effort to delineate

obscuration factors characteristic of the West German theater should

be pursued. Recommended effort is generally described in the various

sections of Plan III. In addition, consideration should be given to

the development of obscurational data for other potential theaters.

Finding 8. A near-nadir viewing angle is desirable for several

reasons, each of which reflects importantly in terms of RPV effec-

tiveness for minefield detection. The obscurational effects of vege-

tation and atmospheric attenuation tend to be minimized at near-nadir

viewing angles. For a given resolution, permissible flight altitude

is maximized at nadir. The unioue signature effects of active IR

52


are most apparent at and near nadir. If a line scanner sensor isdeemed desirable, then nadir or near-nadir viewing is advantageous.

Recommendation 8. The limitations of the present RPV sensor

package in the near-nadir region should be more adeauately explorea

and defined. The effects of these limitations on mine detection per-

formance should be assessed. If substantial performance penalties

are caused by limitations on near-nadir viewing angles or stabiliza-tion system performance, alternative approaches should be explored.

This effort is generally described in Phase 1 and 2 of RPV Plan Ill.

13.5 RPV CHARACTERISTICS

Finding 9. The range, endurance, service ceiling, sortie rate,

survivability, the degree of pointing and trackina stabilization,

viewina angles and payload growth potential appear adeauate for the

minefield detection mission. RPV flight speeds tend to degrade TV

sensor imaaerv (see Finding F).

Recommendation 9. The preliminary findings regarding the above

should be further verified in accordance with the RPV Phases I

through 4 of RPV Plan III.

13.6 DATA LINK CHARACTERISTICS

Finding 10. Data link electronic line-of-siaht recuiremerts are

a limiting factor in connection with low altitude minefield detection

missions.

Recommendation 10. Since proper siting of the remote ground

terminal (RGT) can have a major impact on electronic line-of-sight,

it is recommended that means for obtaining advantageous sitino be

carefully assessed. In particular, the potential of automated ter-

rain analysis currently being developed hv U.S. Army Engineer Topn-

graphic Laboatories should be explored for this application. Effort

to implement this recommendation is included as part of Phases 1, 2

ana 3 of RPV Plan Ill.

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.EIRADAR AND OPTICS DIVISION

Findina 11. The characteristics of the data link may affect thp

fidelity of transmission of minefield detection sensor outputs from

the RPV to the around.

Recommendation 11. Effects of data link on transmission of sen-

sor imagery should be thoroughly investigated. In the event that

imagery is seriously deteriorated bv the data link, approaches to

minimize these effects should be developed. Possible approaches are

the use of on-board pre-processing and the use of line-scanner tech-

niques to reduce imagery bandwidth reouirements. An exploration of

data link effects is included as part of Phases 1, 2 and 3 of RPV

Plan III.

13.7 MAN/MACHINE INTERFACE

Finding 12. With near-nadir viewing, the effect of RPV motion

along its flight path may affect the ability of the sensor or RPV

operator to detect minefields (see Finding 6).

Recommendation 12. Experimentation and analysis should be under-

taken to ascertain whether sensor or RPV operator performance is de-

graded by RPV motion along its flight track. Both continuous and

"snapshot" modes of sensor operation should be considered. EPIM has

proposed an experiment using Array 1 imagery to investigate RPV mo-

tion effects on sensor and RPV operator performance. This effort

should be funded as a priority effort since the utility of the RPV

system as a minefield detection system may hinge on this particular

aspect. Findings from this experiment should serve as a guide for

further determinations regarding RPV motion effects. It should be

noted that in the event that operator performance is seriously de-

graded by RPV motion, there are technioues in the developmental stage

capable of providing operator assist or possibly automatic recogni-

tion of minefields.

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13.8 COMMAND, CONTROL AND COMMUNICATION

Finding 13. A preliminary assessment of command, control and

communication for the RPV system indicates that good and direct link-

ages exist from the RPV sections to brigade maneuver elements di-

rectly concerned with enemy minefields. Similar linkages exist to

the division. RPV sections should be capable of responding in a

timely fashion for scenarios of interest for minefield detection.

Recommendation 13. The initial findings should be verified by a

more comprehensive examiration of command, cortrol and communication.

Such effort is included in recommended Phases 1, 2 and 3 of RPV Plan

III and subsection 5, Study of C31 Implications on Minefield Detec-

tion Systems, of New Concepts/Analysis/Data Base, Plan III.

13.9 FLIGHT REGIMES

Finding 14. There are distinct limitations on flioht reoimes

where minefield detection missions are possible. Using TV or the

planned FLIR sensors, the maximum altitude above ground level wherein

minefield detection is possible is approximately 1860 m. Actual

flights may be constrained to altitudes substantially less than the

maximum due to obscurational factors. The ranae of fields of view

(FOV) available allows operation with maximum swath width down to

approximately 250 m. Minimum flight altitudes are limited by elec-

tronic line-of-sight considerations in connection with the data link.

The RPV section generally is capable of providing both point and

areal coverage over the frontaae normally covered by the hrioade

which it supports. It should be noted that the RPV tracker can im-

pose limitations on coverage.

Recommendation 14. These initial findings should be verified by

a more comprehensive assessment of flight regimes. Means for possi-

ble expansion of permissible flight regimes which will enhance onera-

tion usefulness should also be explored.

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M'RIM RADAR AND OPTIC'S DIVISION

REFERENCES

1. "Operational and Organizational Concept for the Remotely PilotedVehicle (RPV) Target Acauisition and Aerial Rpconnaissance System(TADARS)," Department of the Army, U.S. Army Field ArtillerySchool, Ft. Sill, OK, Draft of January lq79, UNCLASSIFIED.

2. "System Specification for U.S. Army Remotely Piloted VehicleSystem (U)," Specification No. AV-SS-RPV-L 10,000, 10 August1979, UNCLASSIFIED.

3. D. Bornemeier, "Results -- TM-46 Measurements (U)," InternalMemorandum to H. McKenney, Report No. SP-79-692, EnvironmentalResearch Institute of Michigan, Ann Arbor, MI, 13 December1979, UNCLASSIFIED.

4. L.M. Biberman, "FLIR and Active Television: A Comparison ofTheoretical and Experimental Data (U)," Journal of Defense Re-search, Vol. 9, No. 2, Summer 1977, W5765 JDR, Prepared byBattelle Columbus Laboratories for the Defense Advanced ResearchProjects Agency, SECRET.

5. W.L. Wolfe and G.J. Zissis, "The Infrared Handbook (U)," En-vironmental Research Institute of Michigan, Ann Arbor, MI,Chapter 13, 1978.

6. A.C. Lawson, "Climatology of Selected Areas of West Germany Af-fecting Sensor Performance (U)," Report No. 138300-23-T, En-vironmental Research Institute of Michioan, Ann Arbor, MI, June1979, UNCLASSIFIED.

7. D. Bornemeier, et al., "Active Infrared Mine Detection Measure-ments (U)," Report 138300-29-T, Environmental Research Instituteof Michigan, Ann Arbor, MI, August 1979, CONFIDENTIAL.

8. D. Bornemeier, "Array I IR Imagery Analysis (U)," Report No.138300-50-T, Environmental Research Institute of Michigan, AnnArbor, MI, May 1980, CONFIDENTIAL.

9. M. Lopez, "Array I Photo Imagery Analysis (U)," Reoort No.138300-55-T, Environmental Research Institute of Michigan, AnnArbor, MI, July 1980, UNCLASSIFIED.

10. "Minefield Detection Program (U)," Report SP-80-922, Environ-mental Research Institute of Michigan, Notebook prepared forUSAMERADCOM, 22 April 1980 (Plan III).

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'~iRIMRADAR AND OPTICS DIVISION

DISTRIBUTION LIST

U.S. Army Mobility Equipment Research 8 copies

and Development CommandMine Detection DivisionATTN: DRDME-ND (Dr. J.R. Gonano)Ft. Belvoir, VA 22060

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